1. Field of the Disclosure
This invention relates in general to an image forming apparatus, and more particularly, to an image forming apparatus including a system that that is capable of detecting and separating multi-fed sheets whilst allowing individual single sheets to continue feeding.
2. Description of Related Art
Multi-feeds continue to be a problem when separating and feeding sheets from a stack of sheets within the sheet handling industry. A multi-feed occurs when two or more sheets are fed at once and can cause several problems. Typically, a multi-feed will jam somewhere in a machine, either due to the sheets not moving “as one” or timing issues as the sheets aren't exactly on top of one another so the length of the fed sheet appears longer than the machine expects. If the sheets make it through the whole machine the user can find blank sheets within large print runs, or in the case of duplex printing blank sides. All representations of multi-feed are an annoyance to the user and costly in terms of wasted paper and toner on jobs that need to be re-run, the extra electricity consumed in re-running jobs and the cost of time spent by the user either clearing the jam or re-running the jobs. Reducing the number of multi-feeds experienced will improve the overall user experience. Multiple solutions have been advanced for detecting and separating them. Most of the solutions are only capable of dealing with two sheets fed together.
For example, in U.S. Pat. No. 2,892,629 an arrangement is shown in which one of the two rollers between which the sheets pass is positively driven, but the other roller is a retard roller and is not positively driven. The latter roller is freely rotatable on a shaft and is spring urged to turn in a direction opposite to that of the positively driven roller. When only one sheet is passing between the two rollers, the friction is such as to cause the retard roller to turn in the direction of motion of the sheet and against the spring bias. However, when two sheets are disposed between the two rollers, the first sheet, bearing against the positively driven roller, is advanced while the second sheet is moved to the rear, under the influence of the spring biased retard roller which now rotates in the opposite direction to sheet transfer. U.S. Pat. No. 3,895,790 also uses a retard roller arrangement in which the retard roller is reversed when a multiple feed occurs. The prior art devices use a slip clutch system to provide forward movement when a multiple feed is not present. All of these devices depend upon the relative friction between the positively driven roller and the sheet to be advanced as being greater than the friction between the sheet to be advanced and the sheet or sheets to be returned. In U.S. Pat. No. 4,060,232 a garter spring drive is used to rotate a retard roll in a sheet reversing direction when multiple sheets are in a nip formed by a retard roll and a positively driven separator roll. When one sheet is in the nip, slippage occurs between the garter spring and pulleys so that the retard roll turns with the separator roll in a paper feed direction. All of the patents mentioned hereinbefore are included herein by reference.
Even though these solutions are useful, there is still a need for a multi-feed system that will facilitate detection and separation of more than two sheets while reliably feeding sheets one at a time.